Heat Transfer Characteristics and Particle Microscopic-Behavior around a Horizontal Tube Bundle in Fluidized Bed

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The instantaneous heat transfer coefficient, particle volume fraction and particle velocity around a tube in a fluidized bed were simultaneously measured at the same location on the tube surface, using glass beads with average diameter of 0.42 mm and 1.0 mm as a fluidized particle.The heat transfer tube was a phenolic circular cylinder, around which a stainless steel foil with 0.01 mm thickness was stuck to make uniform heat generation on the tube surface. A chromel-constantan thermocouple of 0.012 mm diameter was inserted between the thin foil and the phenolic tube. The instantaneous heat transfer coefficient was estimated from the measured thermocouple temperature, using the inverse heat conduction analysis. This measuring system can respond to a fluctuated heat transfer coefficient with a frequency lower than 40-50 Hz.The particle volume fraction and particle velocity around a tube were measured by the optical fiber probe which was stuck on the tube surface.The measured results were analyzed by the conditional averaging method, distinguishing particle contact from no particle contact. The relationship between the local average heat transfer coefficient and the particle volume fraction during particle contact, on the lower side surface of the tube for the 0.42 mm particle and on all the tube surface for the 1 mm particle, is consistent with the Kunii's large particle model. (The large particle means that its thermal time constant is sufficiently longer than its residence time at the tube surface)